Knee joints are joints which are positioned at a lower end of the thighbone, an upper end of the shinbone, and a rear side of the kneecap (i.e., the patella) to adjust a refraction angle and an extension angle between the thighbone and the shinbone. When a knee is extended, the collateral ligament is tensed, and the lower leg may be disposed linearly with respect to the thigh. On the other hand, when the knee is bent, the lower leg may be extended to allow the lower leg to be moved somewhat in left and right directions.
In general, when a knee is injured such as a damage of the kneecap or an injury of the ligament or osteoarthritis due to aging occurs, knee braces may fix and protect a knee joint region and limit a refraction angle and an extension angle of the knee to prevent a lesion from being progressed (e.g., a collateral damage of the ligament or muscle), thereby smoothly treating diseases. Thus, such a knee brace should be designed so that a motion radius (or a rotation radius) of the knee brace approaches an actual motion radius of a knee joint. Here, a difference between the motion radius of the knee brace and the actual motion radius of the knee joint may cause a collateral injury of wearer. Also, since the wearer can feel easefulness according to the approaching degree, the motion radius of the knee brace may be very important.